Interpretive Summary: We studied three weed control practices (i.e., organic practice of soil cultivation and the conventional practice of glyphosate application) to determine if shifts in weed seedbank composition occurred. After three years of weed treatments, the composition of spring cultivation and fall-spring glyphosate weed communities tended to differ from each other, but the remaining two treatments showed little differentiation. These shifts in the seedbank did not mirror the aboveground weed community composition. Weeds that were dominant in the seedbank were not those that are likely to interfere with grape harvest procedures.

Technical Abstract:
Herbicide and tillage have been shown to influence weed seedbank composition in annual cropping systems, but little information is available for perennial cropping systems like vineyards, where weed control practices are comparatively less intensive. We hypothesized that vineyard weed seedbanks would shift in response to weed control practices, but that the shifts may be slight. We compared the organic weed control practice, soil cultivation, to the conventional practice, applications of the herbicide, glyphosate, in terms of their effects on weed seed bank in a vineyard system. The experiment was conducted in a commercial winegrape vineyard in the Napa Valley of northern California from 2003 to 2005. The vineyard was established in 1996 with Merlot (clone 314) on 110R rootstock (V. berlandieri Planch. X V. rupestris Scheele). The annual treatments were winter-spring glyphosate, spring cultivation, fall-spring cultivation, and fall cultivation-spring glyphosate, and were applied to region under the vine. Weed seedbank composition collected in 2002 prior to treatment establishment differed little among treatments. After three years of weed treatments, detrended correspondence analysis indicated that the composition of spring cultivation and fall-spring glyphosate tended to differ from each other, but the remaining two treatments showed little differentiation. As determined by linear discriminant analysis, the specific weed species were associated with seed banks of certain treatments, yet were not likely to interfere with harvest operations. Vulpia myuros was ubiquitous among treatments, suggesting that the cover crop in the alleys influenced the seedbank. Its distribution between depths in the cultivated treatments also indicated that tillage provided some homogenization of the seed bank along the vertical soil profile. There was little agreement between the emergent seedlings from the seed bank study and those measured annually aboveground in the vineyard, suggesting that greater time is required for this to occur. Furthermore, treatment and microclimatic effects in the field vs. the greenhouse may have influenced germination and the resultant weed community composition